Activator method is a widely practiced chiropractic technique which involves the application of a measured thrust action to pressure points on the body to make adjustments, much like the ancient oriental technique of accupressure. The thrust is provided by a spring-loaded mallet activator instrument with a rubber tip that is positioned at the appropriate pressure point to relieve the improper muscle tension. Determination of where the thrust action is to be applied is made by a number of measurements, an important one of which consists of observing the relative lengths of the patient's legs while the patient is lying on a table. The amount of offset and which leg is longer will give the chiropractor an indication of the degree and source of the patient's misalignment. Typically, however, this "measurement" is inexact because there are no tools available for making a quantitative measurement, and the determination is solely based on the practitioner's visual examination. While the inexact visual estimation method may not significantly impact the quality of treatment, it does limit the practitioner's ability to maintain records of the patient progress or of recurring conditions. Further, where records are required for submission of insurance claims, the ability to provide quantitative measurements would be advantageous.
Leg length comparison for determination of where pressure is to be applied in activator or other chiropractic techniques is effective because the variation in leg length is due to joint displacement caused by muscle tension. Therefore, any variations in muscle tension which induce joint displacement would also be quantifiable using a technique that would be effective in measuring relative leg lengths.
A number of other physiological studies can benefit by using measurements similar to those utilized by chiropractors who practice the activator technique. Among these techniques are applied kinesiology, sacro-occipital technique, Brodie major/minor system (measures arm length), acupuncture point testing, nutritional testing, emotional engram testing, and allergy testing, among others.